This invention relates to a table feed mechanism for a machine tool. In the conventional machine tools where a relative position of work to a tool can be determined along a plural directions (i.e., a X-dir.; a Y-dir.; and a Z-dir.), there are several types of machine tools; one of the types is to drive a tool along the three directions (XYZ-dirs.) and another type is to drive the tool along the two of the directions (for instance YZ-dirs.) and to drive a table for mounting the work along the rest of the direction (for instance X-dir.). In the machine tool of the latter one, it is commonly the case that a nut is fixedly mounted on the table and a feed screw shaft is provided to engage with the inner thread of the nut and then the table is fed by driving the feed screw shaft.
With the aforementioned type of table feed mechanism to feed the table and the work mounted thereon, it is likely the case that the screw shaft is subjected to a great magnitude of tension or compression load due to the inertia force caused by the weight of the object to be fed (including the table and the work) at the time of the acceleration or deceleration operation of the feeding operation. This tension or compression force generated on the feed screw shaft causes the deflection of the shaft that generates an undesirable error in the work path in a non-negligible order. In addition, the inertia force generated on the shaft especially when the shaft being subjected to the acute acceleration and deceleration could also cause the torsional deflection on the shaft. And this torsional deflection of the shaft in turn produces the error in the actual position of the table because of the angular phase position of the drive shaft of the motor will be affected by the torsional deflection.
In order to solve the aforementioned problem of the conventional feeding mechanism of the machine tool, it is natural for the person with ordinary skill in the art to think that increasing the rigidity (including rigidity against the torsional deflection and the rigidity against the bending deflection) of the feed screw shaft to basically strengthen the feed shaft. Furthermore, it is quite natural to think that to gain more rigidity, increasing the diameter of the screw shaft is the simple way. However, the moment of inertia is proportional to the fourth power of the diameter of the torsional shaft, thus slight increase of the diameter of the shaft may significantly increase the moment of inertia. As a result, significantly increased drive power would be required for the motor to drive the thickened screw shaft especially when at accelerating and decelerating procedures. Thus it may necessitate a procurement of a non-standard type larger motor for this purpose, leading a cost increase for the machine tool as a whole and cost reflection upon the products made by the machine tool.